Air filter and method of producing the same

ABSTRACT

To provide an air filter that does not cause holding members to peel even in a high temperature environment, and which can be produced quickly and easily. An air filter (10) includes a filter member (12), holding members (14) disposed at both longitudinal side edges of the filter member (12), and non-woven fabric members (16) for fixing the filter member (12) and the holding members (14). The filter member (12) includes a non-woven fabric of thermoplastic microfibers. The holding members (14) have a bending resistance sufficient to maintain its shape and hold the filter member (12) in its pleated state. The non-woven fabric members (16) have a heat resistance with a melting point not lower than 90° C. and a temporary fixing ability capable of being disposed at the edge portions of the filter member (12) without using a jig.

BACKGROUND OF THE INVENTION

1. Field of Utilization in Industry

This invention relates to an air filter having a pleated filter memberfor filtering contaminated air and to a method of producing such an airfilter.

2. Prior Art

Conventionally, an air filter having a filter member made of asheet-like porous material, such as a paper or a non-woven fabric, hasbeen used as means for filtering contaminated air, which is provided inan air cleaner for home use or for an automobile, a vacuum cleaner, andso forth. Generally, an air filter of this kind is equipped with afilter member obtained by folding the sheet-like porous material into apleat form in order to improve filtering efficiency and service life ofthe filter member. The pleated filter member is held in a predeterminedfolded form by independent holding members that are fixed to the edgeportions of the filter member generally throughout the full lengththereof to realize desired filter effects and to facilitate mounting ata given position or exchanging thereof. The holding members are made ofa sheet-like material having a rigidity sufficient to maintain at leastits own shape. Commercially available adhesives, doublecoated adhesivetapes, heat-fusible films, etc., have been used as a bonding materialfor mutually fixing the holding members and the filter member.

When the air filter described above is used in an apparatus that isexpected to be used in a high temperature environment, such as an aircleaner for an automobile, the bonding material must have a desired heatresistance. In the case of an air cleaner for an automobile, forexample, the bonding material of the air filter must have a heatresistance of not lower than 90° C. If the bonding material is not heatresistant, the bonding material melts under high temperature conditions,so that the filter member and the holding members peel off from oneanother, consequently the filter member cannot hold a pleat form, losinga desired filtering effect. Commercially available double-coatedadhesive tapes, for example, do not have high heat resistance.

On the other hand, in production when the holding members are fixed tothe edge portions of the filter member, which are folded into pleat formand cut into a predetermined dimension, through the bonding material, itis generally necessary to support the filter member and the holdingmembers at predetermined positions by jigs. For example, when thebonding material is made of a heat resistant adhesive (such as an epoxyadhesive), jigs have been used for, respectively, supporting the filtermember and the holding members. The jigs prevent relative movementbetween the filter member and the holding members until the adhesivecures.

When a heat-fusible film, generally made of vinyl acetate, polyamide, anethylene-vinyl acetate copolymer, etc., is used as the bonding material,the holding members are first positioned at the edge portions of thefilter member with the heat-fusible film. The holding members andheat-fusible film are then heated under pressure by, e.g., a hightemperature metal block from the outer face of the holding members,thereby heating and melting the heat-fusible film fixing the filtermember edge portions and the holding members. A heat-fusible film havingthe desired heat resistance, that is, a melting point not lower than 90°C., is not generally tacky. Therefore it is necessary to position andfixedly support the flexible heat-fusible film by jigs at predeterminedpositions along the edge portions of the filter member, which is alsomaintained in the pleated form by a jig unless it can maintain its ownshape under deformation. The film is then clamped between the holdingmembers, which are supported by another jig, and the filter member,followed by heating under pressure. When the heat-fusible film isheated, the temperature and the heating time must be accuratelycontrolled so that the melted film does not flow out.

As described above, problems arise when an air filter is produced usinga heat resistant bonding material. Workability deterioratessignificantly due to the use of jigs for supporting the holding membersand the heat-fusible film. The working time is also increased.

The object of the present invention is to provide an air filter whichcan obtain a desired filtering effect, due to the filter member beingmaintained in a pleated form by holding members which do not peel aparteven under a high temperature environment, not lower than 90° C., whichair filter can be produced quickly and easily without using jigs forfixing and supporting the holding members during the production process.

It is another object of the present invention to provide a method ofproducing such an air filter.

SUMMARY OF THE INVENTION

The present invention employs a construction wherein non-woven fabricmembers, made of polymeric fiber material having a melting point notlower than 90° C., are used as bonding material for mutually fixing afilter member and holding members of an air filter. Accordingly, evenwhen the air filter is used where the filters are expected to be exposedto a high temperature environment such as an air cleaner of anautomobile, the holding members do not peel, and the desired filteringeffect can be maintained while retaining the pleated structure of thefilter member. Moreover, the non-woven fabric member has a temporaryfixing ability whereby it can be disposed on the edge portions of thefilter member without using a jig due to the non-woven fabric membersbulkiness and fibrous surface. The invention air filter can be easilyproduced within a short period of time.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 A perspective view of an air filter according to an embodiment ofthe present invention.

FIG. 2 An exploded perspective view of the air filter shown in FIG. 1.

FIG. 3 A partially cut-away perspective view of an air filter accordingto another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

To accomplish the above objects, the present invention aims at using aheat-fusing non-woven fabric made of a polymeric fiber material that hasboth heat resistance, assuming a melting point not lower than 90° C.,and a temporary fixing ability that ensures engagement with the edge ofthe filter member without the use of jigs.

Therefore, an air filter according to the present invention comprises afilter member, a holding member and non-woven fabric member. The filtermember is formed by folding a sheet-like porous material into pleatform, the material being capable of filtering contaminated air, andhaving a plurality of filter portions connected through bent portions.The holding members, resistant to stretching forces, are fixed to edgeportions of the filter member, generally throughout the full length ofthe edge portions, and hold the filter member in a pleated form whereinthe filter portions are arranged with a predetermined gap therebetween.The holding members can maintain length and width dimensions undertension. The non-woven fabric members are made of a thermoplasticpolymeric fiber material, and arranged between the edge portions of thefilter member and the holding members. The non-woven fabric is at leastpartially melted by being heated to a predetermined temperature so as tomutually fix the filter member and the holding members.

According to a preferred embodiment of the present invention, thenon-woven fabric members comprise melt-blown type non-woven fabricsformed by randomly mixing melt-blown microfibers and crimped staplefibers, both made of thermoplastic polymeric materials, at apredetermined weight ratio. In this case, the melting point of thecrimped staple fibers is preferably higher than that of the microfibers.Further, the filter member may comprise a non-woven fabric having thesame microfibers as those of the non-woven fabric members, and theholding members may comprise a sheet-like fibrous material having abending resistance enabling it to at least maintain its own shape.Furthermore, in view of facilitating the handling thereof, the basisweight of the non-woven fabric members, before heating and melting, ispreferably in a range from 40 to 100 g/m².

Furthermore, the present invention provides a method of producing an airfilter equipped with a filter member made of a sheet-like porousmaterial capable of filtering contaminated air. The method comprises thesteps of folding a sheet-like porous material into a pleated form andthen cutting it to predetermined dimensions so as to form a filtermember; arranging the sheet-like holding members on the edge portions ofthe filter member, while interposing the non-woven fabric members; andapplying a predetermined heat and pressure to the sheet-like holdingmembers from the face opposite the face in contact with the non-wovenfabric members so as to melt at least portions of the non-woven fabricmembers coming into contact with the filter member, and mutually fixingthe filter member and the sheet-like holding members.

According to a preferred embodiment, the method may further comprise thestep of mutually fixing the non-woven fabric members and the sheet-likeholding members before arranging them at the edge portions of the filtermember.

Further, the non-woven fabric members may be formed by randomly mixingmelt-blown microfibers and crimped staple fibers, both made of athermoplastic polymeric material, at a predetermined weight ratio. Inorder to obtain an easy manufacturing process, the microfibers and thestaple fibers may be mixed in a weight ratio ranging from 90:10 to10:90.

The non-woven fabric members may be heated for a period of 60 seconds orless at 200° C.±50° C. in the heating and melting step. When the heatingtemperature is less than 150° C., the adhesion between the filter memberand the non-woven fabric members can be insufficient, and when theheating temperature is more than 250° C., the filter member can beinjured. The heating period may be determined by the adhesion betweenthe filter member and the non-woven fabric members, and how the heatinfluences the filter member. The heating period is preferably 60seconds or less, and more preferably 30 seconds or less, in theabove-mentioned temperature range.

The non-woven fabric members have a bulky and porous structure, as theirgeneral properties, in which a large number of fibrous materials areentangled at random with one another. When the non-woven fabric membersare interposed between the edge portions of the filter member and theholding members, the fibrous materials of the non-woven fabric membersbecome entangled with the edge portions of the filter member,temporarily fixing the non-woven fabric members to the edge portions ofthe filter member. The non-woven fabric members can be easilypositioned, fixed and supported without using a jig necessary forconventional heat resistant fusible films. To heat and melt thenon-woven fabric members, it is necessary only to heat portions of thebulky non-woven fabric members that come into contact with the filtermember. Control of the heating temperature and the heating time isrelatively easy. The thermoplastic polymeric fiber material constitutingthe bonding fibers of the non-woven fabric members generally have asoftening point higher than 90° C. Therefore, an air filter using suchnon-woven fabric members as bonding materials can be suitably used indevices expected to be installed in high temperature environments suchas automobile air cleaners, and the like.

By mixing crimped staple fibers with melt-blown microfiber non-wovenfabric members, the bulkiness of the non-woven fabric members increases,and the temporary fixing effect can be improved. When this crimpedstaple fiber has a higher melting point than that of the microfibers,the microfibers act as bonding fibers. Therefore, the outflow of themelted thermoplastic material can be reliably prevented by controllingthe heating temperature and the heating time in such a manner as to meltonly the microfibers during the heating and melting process. Where theholding members are dimensionally stable non-wovens and the filtermember comprises a non-woven fabric formed of the same microfibers asthose of the non-woven fabric members the edge portions of the filtermember are also partially melted during the heating and melting process.The melted non-woven fabric members can also easily permeate the holdingmembers, thereby further increasing the fixing ability of the non-wovenfabric members. In this case, the non-woven fabric members are alsotemporarily fixed to the holding members, due to the mutual entanglementof the fibrous materials thereof, further improving the workability ofthe heating and melting processes.

The present invention will be explained in more detail with reference topreferred embodiments thereof shown in the accompanying drawings.

Referring to FIG. 1, an air filter 10 according to an embodiment of thepresent invention comprises a filter member 12 folded in a pleated form,a pair of holding members 14 disposed at both longitudinal side edges ofthe filter member 12, and non-woven fabric members 16 disposed betweenthe filter member 12 edge portions and the holding members 14. Thefilter member 12 is preferably formed from a non-woven fabric of fibersmade of a thermoplastic polymeric material, and produced by folding alarge sheet-like non-woven fabric into a pleat form, as shown in FIG. 2,and then cutting it into a desired dimension. Folding the filter media12 into pleat form provides a plurality of filter portions 20 connectedthrough bent portions 18. A preferred polymeric fiber material for thefilter member 12 is polypropylene, e.g., electrostatically chargedpolypropylene. Preferred fibers are melt-blown microfibers and splitfilm electrostatically charged fibers. Alternatively, the filter member12 can be formed from other known filter materials such as paper.

The holding members 14 are sheet-like members, each having substantiallyrectangular surfaces, with one of these surfaces fixed to thelongitudinal side edge portion of the filter member 12 over the fulllength thereof through the non-woven fabric member 16. Accordingly, theholding members 14 hold the filter member 12 in the pleat form, as shownin FIG. 2, where the filter portions 20 are arranged with predeterminedgaps therebetween. The holding member 14 is made of a sheet-like fibrousmaterial resistant to stretching and preferably having a bendingresistance enabling it to maintain at least its own shape. A preferredmaterial is a commercially available carded non-woven fabric made ofacrylic fibers. However, all other materials can be employed so long asthey can fuse with the bonding polymer material of the non-woven fabricmember 16 and can transmit heat for melting fibers of the non-wovenfabric member 16 without melting themselves.

A flexible material can also be used for the holding member 14. In thiscase, the holding member 14 is held in an extended state by a tensioningmeans, while the filter member 12 is fixed to the holding member 14.This is advantageous where it is desirable to fold the filter member 12,prior to using the air filter by bringing the filter portions 20 intocontact with each other. When being used, the filter member 12 isstretched to the shape it had in the fixing step, with the properpredetermined gap between the filter portions 20.

The non-woven fabric members 16 are melt-blown non-woven fabrics formedby randomly mixing melt-blown microfibers and crimped staple fibers bothmade of thermoplastic polymeric materials at a predetermined weightratio. A preferred melt-blown non-woven fabric is described in, e.g.,Japanese Unexamined Patent Publication (Kokai) No. 53-41577. Themicrofiber material forming the non-woven fabric member 16 is preferablypolypropylene, and the crimped staple fiber material is preferably apolyester. The polyester crimped staple fibers further enhance thebulkiness of the non-woven fabric member 16 and improves the temporaryfixing effect. Further, the polyester crimped staple fibers have ahigher melting point than that of polypropylene, therefore, when thenon-woven fabric member 16 is heated and melts, the polyester crimpedstaple fibers can retain the melted polypropylene inside the fibrousstructure preventing an outflow of the melted polypropylene.Alternatively, the non-woven fabric members can be formed ofnon-consolidated or partially consolidated webs of staple fibers andstaple fiber blends by use of a carding machine or Rando™ web machine orthe like.

EXAMPLE

An example of the production process of the air filter 10 will beexplained on the basis of a sample construction, the heat resistance ofwhich was tested by the inventors of the present invention. First, anon-woven fabric made of 100% polypropylene microfibers is folded into afolding height of 30 mm and a folding pitch of 6 mm, and cut into alength of 300 mm and a width of 100 mm, into a pleated state, formingthe filter member 12. Also, a melt-blown type non-woven fabric (thenon-woven fabric member 16) with a basis weight of 100 g/m², made of 65wt % of polypropylene melt-blown microfibers and 35 wt % of polyesterstaple fibers, is laminated to a commercially available carded non-wovenfabric (the holding member 14) with a desired thickness, made of acrylicfibers. The carded non-woven acrylic fiber fabric 14 and the melt-blowntype non-woven fabric 16 are temporarily fixed to each other by themutual entanglement of the fibers thereof. Next, this laminate is cut toa length of 100 mm and a width of 30 mm forming a temporarily fixedlaminate of holding member piece 14 and non-woven fabric member 16.After two laminated pieces are formed, the two pieces are disposed atthe two longitudinal side edge of the filter member 12 so that thenon-woven fabric 16 comes into gentle contact with the side edges. Atthis time, the fibers of the non-woven fabric members 16 becomeentangled with the side edges of the filter member 12 and the fibroussurfaces of the filter portions 20, so that the laminate pieces aretemporarily fixed to the side edges of the filter member 12. In thisstate, a metal block heated to 200° C. is placed on the outside surfaceof the holding members 14. The heated surface is not in contact with thenon-woven fabric member 16. The non-woven fabric member 16 is indirectlyheated for 20 seconds. Consequently, at least portions of thepolypropylene microfibers of the non-woven fabric member 16 are meltedand the filter member 12 and the holding member 14 are fixed to oneanother. When the non-woven fabric members 16 are heated and melted, theedge portions of the filter member 12 are also partially melted, and themelted non-woven fabric members 16 permeate the holding members 14 andreliably fix the holding members 14 to the filter member 12.

In the production process of the air filter as shown in FIG. 3 an airfilter 22 having four holding members 14 fixed to the four surroundingsurfaces is formed by forming four laminate pieces, as described above,disposed on the longitudinal and transverse side edges of the filtermember 12. When the air filter 22 was left standing at 90° C. for 3days, and its heat resistance was tested, peel between the filter member12 and the holding members 14, due to softening or melting of thenon-woven fabric members 16, did not occur at all.

In the production process described above, it is possible to temporarilyfix the non-woven fabric members 16 to the side edge portions of thefilter member 12 and then to temporarily fix the holding members 14 tothe outer surface of the non-woven fabric members 16, instead of usingthe laminated pieces of the holding members 14 and the non-woven fabricmembers 16, temporarily fixed in advance.

We claim:
 1. An air filter comprising:a filter member formed by foldinga sheet of porous material into a pleated form, the material beingcapable of filtering contaminated air, and having a plurality of filterportions connected through bent portions; holding members resistant tostretching forces fixed to edge portions of said filter member forholding said filter member in said pleated form wherein adjacent filterportions are spaced with a predetermined gap forming the pleated form ofthe filter member, and non-woven fabric members made of a thermoplasticpolymeric fiber material said non-woven fabric members arranged betweenthe edge portions of said filter member and said holding members, whichnon-woven fabric members are at least partially melted by being heatedto a predetermined temperature said non-woven fabric members mutuallyfixing said filter member edge portions to said holding members.
 2. Anair filter according to claim 1, wherein said non-woven fabric memberscomprise melt-blown non-woven fabrics formed by randomly mixingmelt-blown microfibers and crimped staple fibers, both made of athermoplastic polymeric material, at a predetermined weight ratio.
 3. Anair filter according to claim 2, wherein the melting point of at least aportion of said crimped staple fibers is higher than that of at least aportion of said melt-blown microfibers.
 4. An air filter according toclaim 1, wherein said filter member comprises a non-woven fabric formedof the same melt-blown microfibers as those of said non-woven fabricmembers, and said holding members comprise a sheet of fibrous materialhaving a bending resistance enabling it to maintain its shape.
 5. An airfilter according to claim 1, wherein the basis weight of said non-wovenfabric members before heating and melting is in a range of from 40 to100 g/m².
 6. A method of producing an air filter equipped with a filtermember made of a sheet of porous material capable of filteringcontaminated air, comprising the steps of:folding a sheet of porousfilter material into a pleated form and cutting it into predetermineddimensions so as to form a filter member; arranging holding members,that are resistant to stretching forces, on edge portions of said filtermember, while interposing non-woven fabric members made of athermoplastic polymeric fiber material between the molding members andthe edge portions of the filter member; and applying a predeterminedheat and pressure to said holding members from a side opposite to theside in contact with said non-woven fabric members so as to melt atleast portions of said non-woven fabric members coming in contact withsaid filter member, thereby mutually fixing said filter member and saidholding members.
 7. A method according to claim 6, comprising the stepof mutually fixing by fiber entanglement said non-woven fabric membersand said holding members before arranging them at the edge portions ofsaid filter member.
 8. A method according to claim 6 or 7, wherein saidnon-woven fabric members are formed by randomly mixing melt-blownmicrofibers and crimped staple fibers, both made of a thermoplasticpolymeric material, at a predetermined weight ratio.
 9. A methodaccording to any one of claims 6 to 2, wherein said non-woven fabricmembers are heated for a period of 60 seconds and less at 200° C.±50° C.in said heating and melting step.